Hide IBMWatsonMapModel object from the outside

[lpatino10]

Internally, any properties that would be of type Map<String, Object> use the wrapper model IBMWatsonMapModel because the base Apex deserializer doesn't support the former.

However, from a developer's perspective, they should be able to set properties that would be of type Map<String, Object> by using the standard Map. It's awkward to have to use an SDK-specific type and prevents things like inline initialization.

Acceptance Criteria:

• Developers are able to set Map parameters using the standard datatype
• Models are still properly serialized/deserialized internally